In commercial food processing and particularly in fast food preparation copious quantities of frying oils and fats are being utilized. Frying of food, such as meat patties, chicken, fish and potatoes, takes place at elevated temperatures and the frying oils and fats, apart from food residues, become contaminated with degradation products of the oils and fats. Simple filtration may remove suspended solids, however it does not take care of dissolved impurities and of the darkened color of the used oils and fats. The dissolved impurities are generally degradation products, such as free fatty acids, aldehydes, ketones, color and odor-forming complex compounds. The presence of these products render the frying oils and fats unsuitable for further use and unless the used oils and fats are purified, health, taste and aesthetic reasons require their disposal.
Several treating agents have been used in the past to purify used oils and fats. Most of these agents, such as clays, magnesium silicates, zeolites, activated aluminas and charcoal, remove one or more of the impurities and/or color bodies. However, none of the known treating agents or composites thereof were found to be fully efficacious for the rejuvenation of used frying oils and fats. As a matter of fact, during treatment some of the acidic treating agents generate free fatty acids, while others, such as magnesium silicate generate soaps, thus the treatment itself is associated with the production of undesired by-products.
It has now been found that a treating composition, consisting of a mixture of acid activated clay or magnesium silicate and gel-derived alumina, accomplishes the desired purification of used frying oils and fats without the disadvantages associated with prior art treating compositions.